Linus Torvalds has announced the release of version 2.6.30 of the Linux kernel. "I'm sure we've missed something, and I know we have some regressions pending. At the same time, we do need the coverage of a eral release, and on the whole it looks pretty good. We've fixed a few regressions in the last few days, and there's always 2.6.30.x." The list of changes is interesting.

I belive in this case the topic is performance regression, which means that while new features was added or other modules/features got optimised one or more existing features got slower , eg uses more cpu cycles to achieve the same work.

Common regressions happens while eg. choosing to optimise towards either latency or throughput, you rarely get to satisfy all users in such a case, which could explain why just about every important module is hot-plugable in the Linux kernel (eg. schedulers optimized for servers vs desktops).